Field of the Invention
The invention relates to compositions for producing porous low-k dielectric films.
Related Art
For certain purposes it is desirable to use materials with low dielectric constants. The manufacture of interlayer dielectric (ILD) semiconductor thin films is typically carried out by depositing the desired thin film on a surface such as a semiconductor substrate. For some applications it is required that the dielectric constant of an ILD film be less than 2.5. One common method of depositing thin films is by spin-on deposition. During spin-on deposition a liquid precursor to the thin film is applied to a semiconductor wafer, and either during deposition or thereafter the wafer is rotated at sufficiently high speed to thin and even the layer of precursor solution. During and after the rapid spinning step the solvents are permitted to evaporate, leaving a dried film of dielectric material.
Spin-on deposition has an advantage over vapor-phase deposition processes in that pore size and geometry may be controllable via a self assembly process in which a detergent that acts as a porogen (or “template”) organizes upon drying and causes the condensed material to yield 2 discrete phases, a silica-rich phase and an organic phase. The organic phase is subsequently removed through an annealing process, leaving behind a porous glassy structure.
It is generally the case that the self-assembly of the detergent phase requires a metal ion catalyst in low concentration (1-100 ppm). If no metal is present the self-assembly process is interrupted and the film that results from condensation and anneal is not sufficiently porous. Consequently the dielectric constant of such a film is higher than desired, and approaches that of condensed silica (˜4).
Alkali metal ions, especially Na+ and K+, are highly effective. However, these ions can contaminate silicon during the semiconductor manufacturing process and cause undesired changes in the performance of electronic devices thusly contaminated. Cesium (Cs+) is an effective substitute for Na+ and K+ and promotes the self assembly of the surfactant template.
However, introducing metal ions into a semiconductor manufacturing facility is something that many companies want to avoid even in cases where there is no known problem associated with Cs in the manufacturing process.